The 29-year Army veteran and sharecropper's daughter from Newton Grove, N.C., is taking over the reins of America's only drill sergeant school in September. She'll be the nation's first female yeller-in-chief.

Not that the premier US training ground for the straight-backed, merciless drill sergeant will suddenly go all soft and cuddly. Her nickname, after all, is "Sergeant Major No Slack." But her appointment does show the Army's growing willingness to put women into gritty warrior slots once reserved just for men.

"This is a male-centric part of the Army," says Sergeant Major King, noting that her appointment "shows that the Army is emerging and … they don't have any reservations about putting the right person where they need to be."

Women have made major inroads into Army leadership since ranks opened in 1976, but top ranks remain partly barred. The Army has 57 women serving as commanders or generals, representing about 5 percent of the commander corps. But the overall percentage of female officers – 15 percent – exceeds the percentage of women in the active-duty ranks, 14 percent.

Most gains have come in the rear echelon, ranging from public relations to human resources – primarily because women are banned from combat positions. The first female four-star general, Lt. Gen. Ann Dunwoody, for example, heads the Army's materiel command.

King acknowledges that the drill sergeant appointment is a special case, representative of the toughest glass ceiling to break: the tight-knit world of the infantry soldier.

That makes her emergence a big step toward breaking boundaries for female leaders in the Army, says Mike Morgan, editor of Army Engineer Magazine.

"[This] is a very significant appointment," writes Mr. Morgan in a recent blog post.

A question-asker from the start

King took a circuitous path to lead the school. Hers is not a military family. The daughter of a disciplinarian sharecropper and father of 13, the self-described "farm girl' faced gasps of disbelief from her siblings as she constantly questioned her father's stern directives – a skill that, counterintuitively, came to serve her well as she rose in the Army's officer ranks, she says.

"That's just how I am, I have to ask a question about what you're saying, because I can't walk away," says King. "That's how I'm wired, and I don't see any reason to change."

King was among the first female recruits to train alongside men when she joined the Army out of high school, in 1980. She began her career as a postal clerk in Germany, spent two years as a drill sergeant, and later joined the Pentagon, hand-picked by then Defense Secretary Dick Cheney.

Her first major leadership test came on 9/11, when she served as first sergeant of the 18th Airborne Corps' headquarters company, responsible for 500 infantrymen, 22 sergeant majors, four colonels, and a slew of other officers. "They didn't care if I was a female," she says. "When I told them to move out, they did."

In a 2008 article for Military Review, Dr. Doll asked whether the Army has truly embraced roles, norms, and values that go beyond gender or whether "it is an unavoidable solidarity, perpetuating male dominance…."

Despite her years of experience, King says she was "amazed" when tapped to lead the school, saying she never thought it was an option. She says Fort Jackson's commander, Brig. Gen. Bradley May, risked ruffling feathers in appointing a woman to the prestigious role.

"More doors are opening in the Army," says King. "It's like I've always been saying: If you hold people to standards and enforce them and know there are no impossibilities, all things are possible unto you."